Recently, a titanium oxide having a monoclinic β-type structure has attracted attention as an active material for nonaqueous electrolyte batteries. In a lithium titanate (Li4Ti5O12) having spinel structure used for conventional nonaqueous electrolyte batteries, the number of lithium ions capable of being inserted is 3 per structural unit represented by Li4Ti5O12.
Accordingly, the number of lithium ions capable of being inserted into Li4Ti5O12 is ⅗ per one titanium ion. Therefore, 0.6 is theoretically a maximum value. On the other hand, in the titanium oxide having a monoclinic β-type structure, the maximum number of lithium ions capable of being inserted into the titanium oxide is 1.0 per one titanium ion. Thus, when such a titanium oxide is used as an active material for nonaqueous electrolyte batteries, the theoretical capacity reaches about 335 mAh/g. Consequently, it appears that the use of titanium oxide having a monoclinic β-type structure allows for development of high capacity batteries.
However, there is a problem such that cycle performance of a nonaqueous electrolyte battery using the titanium oxide having a monoclinic β-type structure is decreased under high temperature.